Here is what you need to know to use the PPK service of the RinexLab.

Quick overview

To use the PPK service, click PPK in the main menu after you logged in. This will open the calculation form.
Name your survey, select the datum in which you want to express the coordinates. Then add up to 4 raw observation files to be processed in the same survey. For each file, indicate the rover name, antenna height, data format, and mode.

Datum

Select here the datum in which the coordinates of the rovers of this survey will be expressed. The possible choices are ETRF2000, RGF93, NAD83, SIRGAS-CON, ETRF2014, RGR92, RGFG95, RGAF09, RGM04, RGSPM06, and ITRF2014. WGS84 is not offered because this datum is not compatible with precision positioning applications. If you are absolutely looking for a rover in this datum, choose ITRF2014, but it is likely that the definition of your project is incorrect. You can contact us for more information.

Antenna height

If you do not specify an antenna height, it will be set to 0.0m by default. The antenna height is the elevation offset between the GNSS antenna and the point for which you wish to obtain the coordinates.

Data format

If you do not know the data format, leave on Auto. The supported formats are as follows: RINEX v2, RINEX v3, UBX, Trimble T01, T02, Leica M00, Septentrio SBF. If your receiver cannot produce raw data in any of these formats, please contact us.

Mode

The determination mode can be kinematic or static. In kinematic mode, a position is expressed for each satellite measurement epoch. This mode is suitable for calculating the trajectory of moving receivers. In static mode, a single solution is provided at the output of the calculation. This mode is suitable for stationary receivers, for example to express the position of a geodetic point precisely.

Add a rover to the survey

To add a rover, click on the plus sign to the right of the grid. You'll be notified if you try to add more than 4 rovers.

Start the process

You must be the owner of a valid PPK token with a positive number of credits to start the processing. Once the survey has been created and the data files associated, you cannot modify it or add rovers. The processing will start automatically. You can find all your surveys and their processing status in the menu PPK > My surveys. You can also see them on a map in the PPK > Surveys map menu.

Use your own base station

You have the choice to use your own base station in the calculation or to let the service do it. In the latter case, we create a virtual station in the centre of the working area. If you want to use your own base, click on the plus sign right to the base part. Then fill in the fields Base name, antenna height, data format, lat/long/h and the raw observation file.

Antenna height

If you do not specify an antenna height, it will be set to 0.0m by default. The antenna height is the elevation offset between the GNSS antenna and the point for which you know the coordinates.

Data format

If you do not know the data format, leave on Auto. The supported formats are as follows: RINEX v2, RINEX v3, UBX, Trimble T01, T02, Leica M00, Septentrio SBF. If your receiver cannot produce raw data in any of these formats, please contact us.

Lat/long/h

Write here the known coordinates of the base in the selected datum, in latitude / longitude / ellipsoidal height format. Latitude and longitude are expressed in decimal degrees, and height in meters. The values are separated by a comma.

The results file

When processing is complete, the result file is available for download from the PPK > My surveys page. There is one zip file per rover. In this archive there is a position / trajectory file in CSV format, and a metadata JSON file. The CSV file contains the position (if static mode) or the trajectory (if kinematic mode) in latitude / longitude / height in the requested datum.

Exemple of a CSV results file for a kinematic process

datetime,lat,lg,h,solution,all,fixed,pdop,sn,se,sh,co_en,co_eh,co_hn
2020-11-25 01:00:00.00,47.946518307,0.180895374,96.7518,FixedL1,26,26,1.6,0.005,0.0041,0.0112,0.0229,0.426,-0.2879
2020-11-25 01:00:01.00,47.946518308,0.180895353,96.7695,FixedL1,26,26,1.6,0.0038,0.0032,0.0087,0.0189,0.4303,-0.2892

The columns are :

  • datetime : date and time of the position [Y-m-d H:M:S.ss]
  • lat : latitude of the rover [decimal degrees]
  • lg : longitude of the rover [decimal degrees]
  • h : ellipsoidal height of the rover [meters]
  • solution : positioning solution, Fixed of Float, basically
  • all : number of satellites in view
  • fixed : number of satellites with fixed ambiguity
  • pdop : PDOP value
  • sn : estimation of the position accuracy in the North-South direction [meters]
  • se : estimation of the position accuracy in the West-East direction [meters]
  • sh : estimation of the position accuracy in the vertical direction [meters]
  • co_en : Eastings/northings correlation coefficient of the coordinates [meters]
  • co_eh : Eastings/height correlation coefficient of the coordinates [meters]
  • co_hn : Height/northings correlation coefficient of the coordinates [meters]

Exemple of a CSV results file for a static process

datetime,lat,lg,h,solution,quality,nsat,amb,pdop,se,sn,sh,co_en,co_nh,co_he
2020-11-25 00:00:00,48.018613671,0.155281902,167.9326,FixedL1,high,11.1,100.0,1.3,0.0031,0.0022,0.0064,0.026,-0.021,-0.009

The columns are slightly different in static mode :

  •  quality : general evaluation of the solution quality, can be high, medium or low
  • nsat : the average number of satellites in view during the observation session
  • amb : percentage of fixed ambiguity during the process
  • pdop : the average value of the PDOP during the observations session

The metadata file

The metadata file gathers the name of the rover, start and end time of the observations session, antenna and receiver types, antenna height, observation rate, and a very important information called "apc". This value tells you if the antenna phase center corrections has been applied during the process. If No, the results are expressed at the antenna phase center, minus the antenna height. If Yes, the results are expressed a the antenna reference point - or APC, minus the antenna height. The APC is often the bottom of mount. If you have any doubt, ask your supplier about this. But be aware that any confusion on this field could lead to a height error between 0 and 20 cm in the results file. The approx_pos value must not be considered as a precise position. It can be used to display the point on a map, but absolutely not to do precise surveying. The leap_seconds value is the delta time in seconds between GPS time and UTC time at the epoch of observation. The conversion between these two time scales can be done with the following formula : UTC = GPS - leap_seconds.

{
    "antenna": "LEIAS10         NONE",
    "antenna_height": 0.0,
    "apc": true,
    "approx_pos": [
        0.180895522,
        47.946518318
    ],
    "ended_at": "2020-11-25 23:59:30 GPS",
    "leap_seconds":18,
    "name": "ARNA",
    "rate":30,
    "receiver": "TRIMBLE NETR5",
    "started_at": "2020-11-25 01:00:00 GPS"
}

The surveys list

You can access the list of your surveys in the menu PPK > My surveys. The list is organised by survey. The name and the date of creation of the survey are displayed in the header. Click on it to scroll down the list of associated rovers. Download the results of the calculation with the download button. You can make a bulk download of the survey by selecting all rovers.
You can search for surveys by name in the dedicated field.

The surveys maps

You can access the map of your surveys in the menu PPK > Surveys map. The markers represent the rovers. In kinematic mode, they represent the position at the first satellite observation time.
By clicking on a marker, you can see its metadata. You can search for surveys by name. Only the results found are then displayed on the map.

What is PPK

PPK stands for Post Processing Kinematic. It is a method of calculating the coordinates of a GNSS receiver that allows centimetric precision in static and kinematic measurements.

The principle of the PPK is to position a GNSS receiver relative to a base station. A distinction is thus made between the rover, the element to be determined, and the base, the element already known in coordinates. The PPK enables the 3D vector between the base and the rover to be calculated very precisely and the rover coordinates can thus be derived. Since the same causes have the same effects, a satellite signal is lengthened in almost the same way when it passes through the atmosphere at intervals of a few kilometres, which is usually the distance between the base and the rover. The algorithm makes use of this property and manages to reduce or even cancel some measurement errors in the GNSS signal by differentiating the common satellite signals between the base and the rover.

The PPK allows the rover's coordinates to be expressed in the base station coordinate system. This system is very often a locally fixed system, to avoid having to calculate the speeds of movement of the points. The current integrated systems are ETRF2000, RGF93, NAD83, SIRGAS-CON, GDA2020, ETRF2014, RGR92, RGFG95, RGAF09, RGM04, RGSPM06, and ITRF2014. If you are looking to obtain positions in WGS84, be aware that this datum is not at all suitable for precision positioning, and you will certainly need to find out a little more about the right datum to use. If you absolutely want WGS84-compliant results, choose ITRF2014, but be sure you know what you're doing.

Where can I use PPK and what datum can I use

The PPK service can be used anywhere in the world if you use your own base station. In case you do not provide your own base station, the PPK service can only be used in the following countries. The list contains the datum you should select when working in the country.

  • Europe : France mainland (RGF93), UK, Ireland, Spain, Germany, Switzerland, Italia, Czech Republic, Austria, Belgium, Luxembourg, Netherlands, Finland, Sweden (ETRF2000 for all)
  • America : USA (NAD83), Brazil (SIRGAS-CON), French Guiana (RGFG95), French West Indies (RGAF09), St-Pierre-et-Miquelon (RGSPM06)
  • Indian ocean : La Réunion (RGR92), Mayotte (RGM04)

We make our best to add more countries to this list. Contact us to ensure that your working area is covered. If ever the datum you usually work with is different from our recommendation, contact your local geodetic authority to know how to convert the coordinates from the RinexLab to the right coordinate system.

What accuracy can I expect

In static mode, you can obtain a precision of a few centimetres in a few minutes of observations. The longer the session, the better the expected accuracy. With a few hours of observations, you can expect 1 cm accuracy. In kinematic mode this is more variable. In good observation conditions, with few signal interruptions, you can also achieve centimetric precision. In both mode, this is highly recommended to work with a multi-band GNSS receiver.

 

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